Manufacturing methods and apparatus for targeted lubrication in hot metal rolling

ABSTRACT

Rolling mill apparatus and methods of hot rolling with targeted lubrication are provided herein. A rolling mill apparatus having multiple roll stacks may include a cooling fluid pump and a lubricant pump fluidly coupled with cooling nozzles and lubrication nozzles through a piping system. The piping system may be configured such that the lubricant pump introduces neat lubricant that mixes with the cooling fluid to form a lubricating fluid as loose lubricant emulsion for discharge to select roll stacks through one or more lubrication nozzles, while one or more cooling nozzles discharge the cooling fluid without the added lubricant. The lubrication nozzles may be aimed to target discharge of the lubricant emulsion to the bite roll. Modifications to mill headers to provide targeted lubrication in accordance with the invention are also provided.

FIELD OF THE INVENTION

The present application claims the benefit of U.S. Provisional Patent Application Ser. No. 61/798,769 filed Mar. 15, 2013, which is hereby incorporated by reference in its entirety.

The present invention relates to manufacturing methods and apparatus for hot rolling sheet metal. In particular, the invention provides manufacturing methods and apparatus having enhanced lubrication for improving the surface quality of rolled sheet metal, such as hot rolled aluminum.

SUMMARY

In one aspect, the invention provides manufacturing methods and a rolling mill apparatus having enhanced targeted lubrication to improve the surface quality of rolled sheet metal and efficiency in production. The invention is particularly useful in hot rolling of aluminum in a rolling mill having multiple stands of rollers.

According to certain aspects, the invention provides delivery of a lubricant, often a poorly-emulsified lubricant, to one or more lubrication nozzles for discharge to the rollers, preferably directed toward the roll nip or bite (e.g. bite nozzles). In one aspect, the poorly-emulsified lubricant is delivered only to specific mill stands, rolls or headers. In certain embodiments, the poorly-emulsified lubricant may be delivered to different mill roll stacks, rolls, or headers in different amounts or compositions. This targeted lubrication allows for improved control of lubrication (e.g. increased or decreased friction) at specific mill stands as needed. In general, the delivery rate of an additional lubricant or lubricant component should be such that it does not exceed the daily addition rate of make-up lubricant. Targeted lubrication with a poorly-emulsified lubricant can rapidly improve the surface quality of rolled aluminum and improve consistency in lubrication during the rolling processing. This feature may also be used to overcome various other mill control problems by either decreasing or increasing friction between the work roll and aluminum strip surfaces as required to control differential friction between aluminum and the top versus bottom work rolls or tension problems created by skidding at some mill stands.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic of a conventional rolling mill.

FIGS. 2A-2B show schematics of aluminum hot rolling tandem mills in accordance with certain aspects of the invention.

FIG. 3 shows a conventional header (shown in view I, II) and a header modified (shown in view III) in accordance with aspects of the invention.

FIG. 4 shows a tandem mill with additional bite spray header in accordance with aspects of the invention.

FIG. 5 graphically exemplifies the effects of lubricants having differing emulsifier concentrations on oil film thickness during hot rolling.

FIG. 6 graphically exemplifies the effect of lubricants having differing oil-water concentration emulsions on oil film thickness during hot rolling.

FIG. 7 graphically compares the hot rolling loads with lubricants used in the form of emulsion with the rolling loads for the same lubricants in the neat form without water.

DETAILED DESCRIPTION

Embodiments of the invention relate to a rolling mill for hot rolling metal, particularly hot rolling of aluminum with a rolling mill having multiple stands of roll stacks and methods for rolling metal, as described herein.

The rolling of metals, such as aluminum, in hot-strip mills is a type of metal forming process that is well known. In a rolling metal forming process, metal stock is conveyed through a pair of rolls known as a roll stack and rolled into a coil or cut into sheets. The type of rolling process is classified according to the temperature of the metal rolled. If the metal temperature exceeds its recrystallization temperature during rolling, the process is termed hot rolling; if the temperature remains below the recrystallization temperature, then the process is referred to as cold rolling. Typically, the metal is rolled through multiple roll stands or stacks of rolls, the sheet of metal reducing in thickness as it passes through each stack and forming a smooth, finished surface. The different stacks may have different configuration or operating condition or applied pressure depending on the process.

FIG. 1 depicts a conventional rolling mill having three roll stacks, Stack A , Stack B and Stack C, through which a sheet of metal 1 is reduced in thickness in a hot rolling metal forming process. Because the incoming metal temperature, friction and deformation of the metal during rolling creates significant heat in the roll of each stack, the mill includes a cooling system that discharges a cooling fluid, such as water but more often lubricating oil emulsion in water, onto the rolls to transfer heat and prevent overheating of the rolls during the metal forming process. Typically, the cooling system includes a coolant pump 10 that pumps the same cooling fluid through various discharge nozzles of the cooling system. The cooling system includes roll coolant headers 23, each containing 2 or 3 rows of nozzles 24 directed toward an inlet side of a roll stack that discharges cooling fluid onto the roll surfaces on an upstream side of the pair of rollers. Some rolling mills may also have coolant nozzles, aiming at the rolls at the metal exit side of each roll stack.

In order to provide a consistent level of friction, a lubricant-in-water emulsion having a relatively low concentration of lubricant is used as a cooling fluid, which is then discharged throughout all nozzles of the cooling system. The emulsified lubricant provides a thin layer of lubricant on the surface of the rolls during rolling. Because the water and lubricant are typically immiscible, to prevent separation and ensure a consistent amount of lubricant delivered with the cooling water, emulsifiers are used to form an emulsification to ensure a more uniform distribution of lubricant within the cooling water. One drawback of such conventional techniques is that certain formulations may require more emulsifiers than would be desirable, since the presence of emulsifiers may reduce overall effectiveness of the lubricant and further increase costs. Another drawback is that the lubricant emulsion is discharged from all the cooling nozzles with limited ability to modify the concentration of lubricant as needed for a particular roller stack or product rolled. Furthermore, typical maintenance of hot mill coolants requires partial dumping of the in-use coolant, as it becomes contaminated. This results in lubricant being wasted proportionally to its concentration in the cooling fluid.

To avoid depositing more lubricant than necessary, a cooling fluid having a relatively low level of emulsified lubricant is generally used. Even when using such techniques, variations in friction may still occur, leading to a poor surface quality of the rolled metal and/or excessive rolling loads with excessive friction or skidding of the work rolls on the metal with inadequate friction. In many conventional systems, once excessive friction or difficulties are observed, an additional amount of lubricant (e.g. oil, synthetic oil, or the like) is injected into the common mill supply coolant line sometimes without emulsifiers for discharge through all the coolant headers and nozzles, a process commonly known as “juicing”). This temporarily addresses the problem by increasing the lubrication layer, thereby reducing friction in the stack roller in which additional lubrication is desired, as well as in each other roller stack. Since the lubricant is incorporated into the cooling fluid throughout the cooling system, in order to avoid exceeding the desirable concentration of lubricant in the coolant, addition of lubricant in this manner can generally only be done for a limited duration or at a very low “juicing rate.” For example, as shown in the experimental results in Table 1, the addition of 330 gallons of the Juicing Lubricant (JL=hot rolling formulation often without emulsifiers) on the suction side of the coolant supply pump over 15 minutes introduces into the cooling fluid flowing to the mill only about 6.25% more oil in form of loose oil droplets. Such a direct lubrication effect, lasts between 10-15 minutes, which is the time equivalent of rolling 2 coils of sheet metal. With a higher Juice Lubricant pumping rate, larger increases in the amount of lubricant flowing to the mill can be produced, for example, adding 9.1% more lubricant over 10 minutes.

TABLE 1 Relative oil concentration increase during hot mill coolant juicing coolant flow rate [GPM] 5,712 oil concentration [%] 8 oil flow rate [GPM] 457 SJ tote volume [Gal] 330 addition/effect time [min] 15 10 SJ flow rate [GPM] 22 33 fraction of oil as SJ [%] 6.25 9.1

Considering the above, rolling with conventional lubrication methods increases costs and decreases throughput, as well as complicates the rolling process since the rolling of some products must be delayed and adjusted when problems associated with insufficient lubrication are observed. This approach may also require re-work or major coolant composition adjustment. Thus, there is a need for a rolling mill apparatus and methods that provide improved consistency and control over lubrication in hot rolling of sheet metal, avoids drawbacks associated with conventional methods, and provides improved rolling without unnecessarily complicating or increasing costs and time associated with the rolling process. In addition, it would be further desirable if such methods or apparatus could be incorporated as a modification or retrofit of a conventional rolling mill.

In one aspect, the present invention allows for targeted lubrication of select roll stacks and/or bite spray nozzles of a hot rolling apparatus, which allows for more consistent lubrication and control over the lubrication in different roller stacks. The improved lubrication, allowed by embodiments of the invention, provides improved surface quality and increases throughput and efficiency in production. In certain aspects, targeted lubrication includes delivery of a poorly-emulsified lubricant (possibly but not necessarily with little or no emulsifier-agents) to lubrication nozzles directed toward the roll nip of the roller stack (bite sprays), the lubrication nozzles for a particular stack being fed by a header. Because the delivery of the additional lubricant, in these aspects, is targeted only to the bite sprays and only to the specific headers, the total amount of lubricant delivered is lower than that under present “non-targeted” juicing practices. This allows “targeted lubrication” or “juicing” to be used for a longer time period, thereby improving surface quality of a larger number of coils. For example, with a 330 GPM bite spray flow through both nozzles, the direct effect of the same 330 gallons of Juicing Lubricant can be extended to 188 minutes (assuming the injection rate producing 6.25% of additional oil as related to the oil originally-present in the coolant) or can be extended to 125 minutes with the injection rate producing 9.1% of additional oil. These increases in the duration of the effect would allow improved rolling daily production of can-end stock (CES) coils or other surface sensitive alloys that usually require conventional juicing techniques.

Embodiments of the invention, in accordance with the above described aspects, are depicted in FIGS. 2A-4. FIG. 2A illustrates a rolling mill that provides targeted and controlled delivery of lubricant to Stack A. The piping system has been modified such that the work roll cooling discharge nozzles that previously discharged the same cooling fluid through all banks of nozzles (coolant and bite sprays) are configured to discharge a loose-emulsion of lubricant formed in a static mixer through the bite spray nozzles and cooling fluid through the coolant nozzles.

The rolling mill configuration in FIG. 2A, similar to that in FIG. 1, has been modified to provide targeted delivery of lubricant to select roller stacks. The rolling mill includes a separate lubrication pump 20 and cooling fluid pump 10. The cooling fluid pump 10 is fluidly coupled with the coolant spray set of nozzles 24 of the header 23 for each stack through a piping system. The piping system includes an in-line mixer 22 at select stacks to allow formation of the loose-emulsion for discharge at the select stack when desired. In this embodiment, the mill is configured with a set of bite lubrication nozzles 25 at the inlet of Stack A that discharge coolant directly toward the bite of the rolls of Stack A and the rolled metal 1. The lubrication pump 20 is fluidly coupled to the bite lubrication nozzles 25 through a lubrication section of the piping system that includes the in-line static mixer 21. Rather than introducing a lubricant emulsion into the supply line of the cooling fluid, the lubricant is introduced into the lubrication section through a separate line and mixes in the in-line mixer 22 with the cooling fluid. The introduction of lubricant into the coolant flow is selectively controlled through valve 21. The lubricant mixes with the cooling water to form a loose emulsion, which is an emulsion that contains relatively large lubricant droplets that can coalesce and separate from cooling water. The loose emulsion is then discharged through the lubrication nozzles to the rolls of the select roll stack, in this embodiment, discharged to the roll bite through the bite lubrication nozzles 25. Thus, by selectively introducing lubricant into the in-line static mixture the lubrication at the roll bite can be readily controlled throughout the rolling process without otherwise altering the flow or composition of the cooling water discharged through the remaining nozzles.

In an operating model of an example rolling mill, the system design assumes 330 GPM bite spray coolant flow and up to 3 GPM injection of the poorly-emulsfiable oil (“juice lubricant”) at an operating pressure of 150 psi. Given these operating characteristics, a static mixer with a 4″ diameter and a 40″ length allows sufficient incorporation of the injected oil and cooling water to form a loose-emulsification for discharge through the lubrication nozzles. The calculated linear velocity of coolant flow through the mixer would be 8.3 ft/s with a pressure drop 5.5 psi. Generally, a 1 ft/s minimum flow rate is recommended to maintain turbulent flow in the static mixer, although for most blending applications a 2-3 ft/s flow rate should be sufficient. In some embodiments, a 7-8 ft/s flow rate might be particularly suited to create liquid-liquid dispersions. It is appreciated that mixers of various sizes and shapes may be used in accordance with the principles of the present invention. Generally, a pump 20 capable of delivering 3 gallon per minute lubricant flow at 170 psi pressure would be suitable to inject the neat lubricant in front of the static mixer, although various other pumps may be used depending on the particular system and associated operational characteristics. Prior to the lubricant injection port, part of the mill coolant stand supply stream is split from the typical 6″ or 8″ stand coolant supply line into a separate bite spray supply line of the smaller diameter, such as a diameter of 4,″ which is equipped with the static mixer pipe 22. The juicing lubricant is supplied from the neat lubricant tank and injected into the bite spray supply line right upstream of the static mixer. Typically, this utilizes a specially-selected pump having the appropriate pressure and a precisely-controlled flow rate. The lubricant is mixed with the coolant in the static mixer 22 and then carried by the bite spray coolant stream to the header 23 and discharged through the bite spray nozzles 25.

In other aspects, the milling system is adapted to allow targeted delivery of the lubricant between two or more roller stacks of a rolling mill. In some embodiments, the system may include multiple lubricant pumps, each fluidly coupled with the lubrication nozzles at one or more stacks or at different roller stacks. This feature allows delivery of differing amounts and/or type of lubricants to one or more select stacks. In other embodiments, the system may include one or more additional valves between the lubricant pump and the lubrication nozzles associated with each stack, such that adjustment of the one or more additional valves allows for differing amounts/concentrations of lubricant to be delivered to one or more stacks, to different stacks or to be varied during the rolling process as needed. Adjustment of the one or more valves may be performed either by user input command or by an automatic control algorithm based on various operating characteristics.

FIG. 2B illustrates another embodiment in which the piping system includes a static mixer 22 at multiple stacks to allow selective lubrication, as needed, at a particular roll stack. The piping system has been modified such that the work roll cooling discharge nozzles that previously discharged the same cooling fluid through all banks of nozzles (coolant and bite sprays) are configured to discharge a loose-emulsion of lubricant formed in the static mixer 22 through the bite spray nozzles at each stack, while cooling fluid continued to discharge through the coolant nozzles. By use of valves 21, the juice lubricant is selectively introduces so that the loose-emulsion is formed for discharge only at the selected stacks. This may be useful during a rolling procedure in which additional lubrication is desired at a roll bite of downstream nozzles at certain points during the rolling process. In addition, the lubrication at each stack can be readily adjusted, either manually or automatically, in response to observed or determined excessive friction or slipping at a particular stack.

Since the lubricant delivery is targeted, the lubricant can be delivered where it will have the largest impact on the rolled metal surface quality and rolling performance of the rolling mill. For example, reroll surface quality on most mills can be markedly improved by aiming the bite/lubrication coolant sprays into the roll nip. In addition, during rolling only some stands may operate under lubrication starvation condition, leading to poor surface finish. Based on the empirical data shown in the graphs in FIGS. 5 and 6, the optimal lubricant thickness on the rollers may vary according to the rolling speed. Stands with higher rolling speeds may have an insufficient amount of lubricant released on the rolls or in the roll nip. It is also possible that on some stands roll nip temperature might be so high that lubricant is volatilized and degraded. The present invention allows additional lubricant to be delivered to rolls having higher rolling speeds, without “juicing” the cooling fluid for the other stands or the entire cooling supply line.

Many conventional hot rolling mills utilize cooling and bite lubrication spray nozzle banks In such rolling mills, both types of nozzles are fed from a common cavity in the coolant header. In one aspect, the invention provides a modified header in which the header chamber and control logic may be modified to allow separate feeds to the cooling spray cavity and to the bite spray cavity, valves and nozzles. For example, the modified header may include a separation within the header cavity to define a first portion separate from a second portion such that input of cooling water into the first portion of the header cavity that feeds the cooling discharge nozzles does not mix with lubrication fluid in the second portion that feeds the bite lubrication nozzles. As shown in the example of FIG. 3, a conventional header 23′, such as that shown in view I, includes one or more inlets i through which cooling water is supplied for discharge through the nozzles 24, 25. As can be seen in the cross-sectional view (II), the conventional header 23′ includes a common header cavity such that cooling fluid within the cavity is common to all discharge nozzles. A modified mill header 23, such as that shown in view III, allows for separate feeds to cooling discharges nozzles 24 and bite lubrication nozzles 25 by use of a separation between the lower part of the header cavity (for bite spray) and the top cavity (for coolant spray). Since many conventional rolling mills include two banks of cooling nozzles and one bank of bite spray/lubrication nozzles, the modified header includes port or ports feeding the header cavity connected through inlet valves i₁ to each of the two banks of cooling nozzles, separate from a port or ports feeding the header cavity connected through valves i₂ to the bite spray/lubrication nozzle bank. The separation between the ports and header cavities allows feeding of the cooling nozzles and the bite lubrication nozzles with two different fluids. This modified mill header can readily replace a conventional mill header, thereby allowing retrofitting of convention mills to provide targeted lubrication in accordance with the principles of the present invention.

In another aspect, the system may include additional modifications to provide targeted roll bite lubrication in conventional mills that do not already have bite sprays. On mills without bite sprays and with level control of cooling, the “targeted lubrication” concept can be explored in only limited way by injecting additional lubricant into lines feeding entry headers of the individual stands. In this case the lubrication effect would likely be diminished and its duration reduced in proportion to the coolant flow rate through these headers, as shown below in Table 2. To accommodate additional coolant flow without excessive pressure drop, the size of the static mixer may be increased. For example, a static mixer device having a 6″ diameter and a length of 60″ may be used to accommodate 1100 GPM coolant flow with 11 psi pressure drop, and a size of the oil injector pump can be increased to handle 6-9 GPM of additional poorly-emulsified oil.

TABLE 2 Direct lubricating effect of the injected oil during targeted lubrication through selected entry side coolant headers or dedicated bite sprays Time to deliver Flow Rates [GPM] 330 gal [min] U at U at U at U at Header 6.25% 9.1% 6.25% 9.1% Location Coolant Oil of oil of oil of oil of oil F1 Entry 731 58 2.8 2.1 117 156 F1 Delivery 1109 F2 Entry 1109 89 4.3 3.2 77 103 F2 Delivery 1109 F3 Entry 1109 89 4.3 3.2 77 103 F3 Delivery 545 Additional 330 26 1.3 1.0 260 346 bite spray

The advantages of targeted lubricant delivery can be further realized by directing or focusing lubricant delivery on the rolling nip of the rollers and metal sheet. Since conventional rolling apparatus often include lubricating nozzles that discharge generally towards the rollers and not towards the roll bite, such apparatus can be modified in accordance with aspects of the invention to further target delivery of lubricant to the nipping part or bite. For such mills that lack bite sprays and with level control of cooling, suitable headers can be engineered and installed that provide a discharge stream mixed with lubricant and directed to the roll bite. FIG. 4 depicts retrofitting of bite sprays into the tandem mill without the bite sprays, showing modifications to guide plates and additional shielding that direct the discharge mixed with lubricant to the roll bite. The lubricant may be delivered in various ways, such as being fed directly through the header, being delivered as a loose-emulsion from a bulk lubricant tank through an in-line mixer, or delivery by any other means suitable for mixing with a bite spray coolant stream at one or more select stacks.

In another aspect, the system may include two separate sections for the top and bottom rolls such that the targeted lubrication may differ between the top surface of the strip metal and the bottom surface of the strip metal during rolling. This aspect may be used to provide improved control over surface quality as well as control of friction between the top and bottom side of the slab.

FIGS. 5-7 demonstrate the advantages of using a neat lubricant or a loose emulsion with little or no emulsifier agents in a rolling mill in accordance with aspect of the invention. FIG. 5 illustrates the effect of non-ionic emulsifier concentration at 50° C. on oil film formation (data source: Cambiella, A., Benito, J. M., Pazos, C, Coca, J., Ratoi, M, Spikes, H. A., Tribol. Lett. 22, 53-65, 2006). FIG. 6 illustrates the effect of the oil-water concentration in emulsions on oil film formation (data source: Yang, H., Schmid, S. R., Reich, R. A., Kasun, T. J., Tribol. Trans. 47, 123-129, 2004). FIG. 7 illustrates rolling loads measured on the laboratory rolling mill with neat lubricants and their associated oil-in-water emulsions, the distance from the diagonal to each data point increases along with increasing differences in anti-friction properties between the neat oils and their corresponding emulsions.

As compared to the coolant emulsions (cooling fluids) used in the cooling supply line in conventional mills, delivery of a small quantity of a loose emulsion (poorly emulsified lubricant including an oil-water combination with little or no emulsifying agents) offers distinct improvements in lubrication. Particularly when delivered into the roll bite of a select roll stack, such an emulsion provides improved anti-friction properties and reroll surface quality. Studies have shown that the amount of oil delivered from oil-in-water emulsions into the tribological contact between a flat disk and a ball increases with the decreasing amount emulsifier and increasing concentration of oil, such as indicated in FIGS. 5 and 6.

As shown in FIG. 7, lab results indicated that hot rolling on neat lubricants provides stronger anti-friction effect than coolant emulsions and unstable or loose emulsions (i.e., with large oil droplets) provide better lubrication (oil release) than stable emulsions (with small oil droplets). Moreover, injecting a small amount of lubricant without emulsifiers (“juice,” “super juice,” “juice lubricant”) into the mill coolant supply line (“juicing”) has demonstrated rapid improvements of surface quality of the reroll in hot mills. Thus, the targeted lubrication with a loose emulsion, as provided by the present invention, allows for improved surface quality more consistently during the rolling process. In addition, the hardware required for targeted lubricant delivery into the coolant (“targeted lubrication”) can be easily modified to feed hot water or hot water with emulsifiers selectively into select bite sprays. This should result in the increase of friction, allowing mill threading without refusals as well as control of differential friction such as between top and bottom rolls and between stands. Thus, the principles of the present invention may be used to modify conventional rolling mills and provide the advantages and benefits described herein.

Various embodiments of the invention have been described in fulfillment of the various objectives of the invention. It should be recognized that these embodiments are merely illustrative of the principles of the present invention. Numerous modifications and adaptations thereof will be readily apparent to those skilled in the art without departing from the spirit and scope of the present invention as defined in the following claims. 

What is claimed is:
 1. A sheet metal rolling apparatus, said apparatus comprising: at least one rolling stand having a pair of rolls between which a sheet of metal is rolled to reduce its thickness, wherein the pair of rolls includes a top roll and a bottom roll; a set of lubricating bite nozzles adapted to discharge a lubricating fluid produced by mixing a cooling fluid with a juice lubricant at an inlet side of each top and bottom roll of the pair of rolls, the set of lubricating bite nozzles comprising one or more lubricating bite nozzles aimed at a roll bite area of the pair of rolls and the sheet of metal; a set of cooling nozzles adapted to discharge a cooling fluid onto a roll surface of the top roll above the bite spray and discharge the cooling fluid onto a roll surface of the bottom roll below the bite spray, the set of cooling nozzles comprising one or more cooling nozzles; a cooling fluid pump that pumps the cooling fluid to the one or more cooling nozzles through a piping system; a lubricant pump that pumps a juice lubricant into the piping system, the piping system being configured such that the juice lubricant mixes with the cooling fluid to form the lubricating fluid before discharge through the one or more lubricating bite nozzles while the cooling fluid flows to the cooling nozzles.
 2. The sheet metal rolling apparatus of claim 1, wherein the piping system includes a cooling section and a lubricating section, the cooling section fluidly coupling the cooling fluid pump to the cooling nozzles, and the lubrication section fluidly coupling the lubricant pump and coolant pump to the bite lubrication nozzles.
 3. The sheet metal rolling apparatus of claim 2, wherein the lubricating bite nozzles are configured such that fluid discharged therefrom is aimed at a roll bite where the pair of rolls contacts the sheet metal.
 4. The sheet metal rolling apparatus of claim 2, wherein the lubrication section includes a static, in-line mixer disposed between the valve and the lubrication nozzles such that the cooling fluid and the lubricant mix within the mixer to form an emulsification of the cooling fluid and the lubricant for discharge through the lubrication nozzles.
 5. The sheet metal rolling apparatus of claim 1, further comprising: a mill header having a lubrication fluid chamber and a cooling fluid chamber, the chambers being separate, wherein the lubrication fluid chamber is fluidly coupled to the lubrication nozzles and the cooling fluid chamber is fluidly coupled with the cooling nozzles.
 6. The sheet metal rolling apparatus of claim 1, wherein the apparatus is adapted for hot rolling of sheet aluminum.
 7. The sheet metal rolling apparatus of claim 1, wherein the cooling fluid comprises water or dilute and tight water-in-oil emulsion and the lubricant comprises oil.
 8. The sheet metal rolling apparatus of claim 1, wherein the at least one roller stand comprises two or more stands, each having a pair of rolls between which the sheet of metal is rolled to reduce its thickness after being rolled through the first stand of rollers; one or more additional sets of lubricating nozzles adapted to discharge a lubricating fluid at an inlet side of the pair of rollers of one or more selected mill stands, each of the one or more additional sets including lubricating nozzles coupled to both the lubricant pump and the cooling fluid pump through the piping system.
 9. The sheet metal rolling apparatus of claim 1, wherein the lubricating nozzles deliver bite sprays.
 10. The sheet metal rolling apparatus of claim 1, wherein the first set of lubricating nozzles comprise one or more fluid discharge nozzles that direct fluid discharged from the discharge nozzles toward a nipping part of the pair of rollers.
 11. The sheet metal rolling apparatus of claim 1, wherein the piping system is configured such that a concentration of the lubricant and cooling fluid discharged from the cooling nozzles is different than that of a concentration of the lubricant and cooling fluid discharged from the set of lubrication bite nozzles.
 12. The sheet metal rolling apparatus of claim 1, wherein the piping system is configured such that a composition of the lubricant in the lubricating fluid and of the lubricant in the cooling fluid are different.
 13. The sheet metal rolling apparatus of claim 1, wherein the piping, valves and juice lubricant pumping system is configured such that lubricating fluid may contain a different lubricant concentration and composition on each mill stand.
 14. A method of sheet rolling, said method comprising: rolling a sheet of metal between a pair of rolls of a metal rolling apparatus; and lubricating an interface between the metal rolled and each roll of the pair of rolls with a lubrication fluid during rolling, the lubrication fluid comprising a mixture of a cooling fluid and a juice lubricant, the cooling fluid and juice lubricant being pumped into a piping system by a cooling fluid pump and lubrication pump, respectively, and mixed within the piping system before discharged through a set of lubrication bite nozzles.
 15. The method of claim 14, further comprising: mixing the lubricant and cooling fluid in the piping system within a static mixer to form a loose emulsion of lubricant and cooling fluid.
 16. A method of claim 14, said method further comprising: rolling the sheet of metal between a pair of rolls of one or more additional stands of the metal rolling apparatus after rolling through the first stand; lubricating an interface between the metal rolled and each of the pair of rollers of any selected or all mill stands with a lubrication fluid during rolling.
 17. The method of claim 16 wherein the mixture of lubricant and cooling fluid discharged from the lubrication bite nozzles is the same on each mill stand.
 18. The method of claim 16 wherein the mixture of lubricant and cooling fluid discharged from the lubrication bite nozzles is different on each mill stand.
 19. The method of claim 16 wherein the apparatus comprises at least two roll stacks, each comprising a pair of rollers and associated lubrication bite nozzles, wherein the piping includes a static mixer between a juice lubricant source and the lubrication bite nozzles for each roll stack, the method further comprising: selectively lubricating a selected roll stack by introducing juice lubricant into the static mixer associated with the lubricant bite nozzles for the selected roll stack.
 20. The method of claim 16 wherein the apparatus comprises at least two roll stacks, each comprising a pair of rollers and an associated set of lubrication nozzles, each set of lubrication nozzles having a header, the method further comprising: selectively lubricating a selected roll stack by introducing juice lubricant into the header of the set of lubrication nozzles associated with the selected roll stack. 